Near-infrared Digital Images Research Articles

Evaluation of near-infrared digital imaging transillumination compared with bitewing radiography for proximal caries detection in children.

Limitations in traditional caries detection tools have driven the development of alternatives methods, focused on the early lesion detection such as near-infrared digital imaging transillumination (NIDIT). The aim of this study was to evaluate the performance of NIDIT compared with bitewing radiography (BWR) in the detection of interproximal carious lesions in children. A retrospective audit of data from children who had NIDIT, BWR and intraoral photographs was conducted. Carious lesions were scored on a tooth surface level with BWR acting as the primary reference for comparison. Accuracy was determined using multi-class area under the curve (AUC), and correlation was determined using Fleiss' Kappa. Data from 499 tooth surfaces involving 44 children were included in this study. The average age across the participants was 86 months (~7 years) with an average dmft (decayed, missing and filled teeth in primary dentition) of 5.29. Multi-class AUC comparing NIDIT to BWR was 0.70. The correlation between NIDIT and BWR was moderate (0.43), whereas the correlation between photographic examination and BWR was 0.30, which is fair. When compared to BWR, NIDIT showed a high specificity but a low sensitivity for proximal caries detection in primary teeth.

Reflectance calibration of UAV-based visible and near-infrared digital images acquired under variant altitude and illumination conditions

The understanding of the radiometric response of visible and near-infrared cameras is important for quantitative spectral information obtainment. There is a lack of information regarding the comparison of calibration approaches of near-infrared images of digital cameras, since the Bayer Filter is not usually removed and the obtained NIR image records the infrared radiation in three different spectral bands (red, green and blue). This article aimed at developing reflectance calibration models for UAV-based visible and near-infrared (processed under four different methodologies) digital images acquired under variant altitude and illumination conditions. Reflectance calibration models were developed for red, green, blue and near-infrared spectral bands using UAV-based digital numbers – DNs (acquired in twelve UAV flights under variant altitude and illumination conditions) and laboratory-based reflectance. The variation of DNs among flight conditions represents from 12% to 17%, depending on the spectral band. For the visible bands, all reflectance calibration models presented R2 superior than 0.94. Regarding the near-infrared bands, the grey scale and green channel approaches demonstrated the best results, with R2 between 0.89 and 0.98. The validation of the developed models, assessed by the correlation between reflectance measured in field and the predicted reflectance, revealed strong correlations between the observed and predicted reflectance for the visible bands and for the near-infrared grey scale and green channel approaches, which were found to be more suitable for the calibration of near-infrared digital images into reflectance.

Semiautomatic detection and classification of materials in historic buildings with low-cost photogrammetric equipment

Abstract The detection of materials and damage in building facades by means of near-infrared digital images is not a widely explored field in architectural research, especially in rehabilitation and historic building surveys. The aim of this work is to study whether spectral classification image methods, which are frequently used in remote sensing land applications (non-contact geophysical techniques), could be applied in the architectural field to detect various construction materials in historic building facades by means of low-cost photogrammetric equipment. Several classification methodologies were applied to different image band combinations, which led to the conclusion that the highest accuracy is obtained with a multiband image composed of visible and near-infrared bands. We also performed a derived measurement of the real surface of the facing material, demonstrating that low-cost instrumentation could be useful in architectural interventions in cultural heritage to identify construction materials in a non-destructive way.

Alternative methods to visual and radiographic examinations for approximal caries detection.

A shift in caries prevalence from occlusal surfaces to approximal surfaces has been demonstrated by epidemiological studies. Two recent meta-analyses evaluated the performance of visual examination and radiography for carious lesion detection, and reported low sensitivity but high specificity for early approximal caries detection. This suggests that the conventional methods have a higher risk of failing to detect approximal lesions. Consequently, in caries susceptible populations, there is a risk of progression of non-cavitated lesions to irreversible tooth destruction before the lesions are detected. This paper aims to review the performance of unconventional and novel methods for approximal caries detection. In vitro and in vivo studies identified through a MEDLINE search using keywords such as caries detection, approximal caries detection, light fluorescence and dental caries, and transillumination and dental caries were reviewed. The unconventional methods known to be used for approximal caries detection and included in this review are: cone beam computed tomography, fiber-optic trans-illumination, digital imaging fiber optic trans-illumination, near-infrared digital imaging transillumination, optical coherence tomography, laser fluorescence, ultrasound, and LED reflection and refraction.

A combined colour-infrared imaging technique for measuring water surface over non-horizontal bottom

This paper presents a combined colour-infrared imaging technique based on light refraction and absorption for measuring water surface over a non-horizontal fixed bottom known a priori. The procedure requires processing simultaneous visible and near-infrared digital images: on the one hand, the apparent displacement of a suitable pat- tern between reference and modulated visible images allows to evaluate the refraction effect induced by the water surface; on the other hand, near-infrared images allow to perform an accurate estimate of the penetration depth, due to the high absorption capacity of water in the near-infrared spectral range. The imaging technique is applied to a series of laboratory tests in order to estimate overall measurement accuracy. The results prove that the proposed method is robust and accurate and can be con- sidered an effective non-intrusive tool for collecting spa- tially distributed experimental data.

The spatially resolved characterisation of Egyptian blue, Han blue and Han purple by photo-induced luminescence digital imaging

The photo-induced luminescence properties of Egyptian blue, Han blue and Han purple were investigated by means of near-infrared digital imaging. These pigments emit infrared radiation when excited in the visible range. The emission can be recorded by means of a modified commercial digital camera equipped with suitable glass filters. A variety of visible light sources were investigated to test their ability to excite luminescence in the pigments. Light-emitting diodes, which do not emit stray infrared radiation, proved an excellent source for the excitation of luminescence in all three compounds. In general, the use of visible radiation emitters with low emission in the infrared range allowed the presence of the pigments to be determined and their distribution to be spatially resolved. This qualitative imaging technique can be easily applied in situ for a rapid characterisation of materials. The results were compared to those for Egyptian green and for historical and modern blue pigments. Examples of the application of the technique on polychrome works of art are presented.

Visible and near-infrared digital images for determination of ice velocities and surface elevation during a surge on Osbornebreen, a tidewater glacier in Svalbard

A field of vectors showing the average velocity of the surging glacier Osbornebreen, Svalbard, was determined by comparing sequential SPOT (Système pour l’Observation de la Terre) and Landsat thematic mapper images. Crevasses which developed during the initial phase of the surge in the winter of 1986–87 were tracked using a fast Fourier chip cross-correlation technique. A digital elevation model (DEM) was developed using digital photogrammetry on aerial photographs from 1990. This new DEM was compared with a map drawn in 1966. The velocity field could be almost entirely determined with 1 month separation of the images, but only partly determined with images 1 year apart, due to changes of the crevasse pattern. The velocity field is similar to that found for Kronebreen, a continuously fast-moving tidewater glacier. No distinct zones of compressive flow were present and the data gave no evidence of a compression zone/surge front traveling downstream. The velocity field, the rapid advance of the terminus and the development of transverse crevasses in the upper accumulation area within a 6 month period may indicate that the surge developed as a zone of extension starting near the terminus and propagating quickly upstream. The crevasse pattern in the images is therefore interpreted to be the result of the extension zone traveling upstream, and, as the whole glacier starts to slide, the crevasse pattern alters according to the bedrock topography.

Visible and near-infrared digital images for determination of ice velocities and surface elevation during a surge on Osbornebreen, a tidewater glacier in Svalbard

A field of vectors showing the average velocity of the surging glacier Osbornebreen, Svalbard, was determined by comparing sequential SPOT (Système pour l’Observation de la Terre) and Landsat thematic mapper images. Crevasses which developed during the initial phase of the surge in the winter of 1986–87 were tracked using a fast Fourier chip cross-correlation technique. A digital elevation model (DEM) was developed using digital photogrammetry on aerial photographs from 1990. This new DEM was compared with a map drawn in 1966. The velocity field could be almost entirely determined with 1 month separation of the images, but only partly determined with images 1 year apart, due to changes of the crevasse pattern. The velocity field is similar to that found for Kronebreen, a continuously fast-moving tidewater glacier. No distinct zones of compressive flow were present and the data gave no evidence of a compression zone/surge front traveling downstream. The velocity field, the rapid advance of the terminus and the development of transverse crevasses in the upper accumulation area within a 6 month period may indicate that the surge developed as a zone of extension starting near the terminus and propagating quickly upstream. The crevasse pattern in the images is therefore interpreted to be the result of the extension zone traveling upstream, and, as the whole glacier starts to slide, the crevasse pattern alters according to the bedrock topography.